The present invention relates to a photosensitive body for electrophotography (henceforth referred to as simply "photosensitive body") used in electrophotographic copiers, digital copiers, printers, and the like. More specifically, the present invention relates to a laminated organic photosensitive body, in which the layers have separate functions. This laminated organic photosensitive body is provided with a charge generating layer and a charge transport layer, containing a specified electron transport compound, on a conductive substrate.
An electrophotographic photosensitive body has a basic construction of a photosensitive layer, which has a photoconductive function, laminated on top of a conductive substrate. In recent years, because of its advantages in variety, high productivity, safety, and the like, research and development have been actively conducted in organic electrophotographic photosensitive bodies which use organic compounds as the functional components for generating and transporting charge. There have been advances in their application in copiers and printers.
Photosensitive bodies must have a function for maintaining surface charge in the dark, a function for receiving light and generating charge, and a function for transporting the generated charge. There is what is called a single layer photosensitive body, which is equipped with a single layer photosensitive layer having all of these functions. There is also a function-separated laminated photosensitive body, which is equipped with a photosensitive layer in which layers having separate functions are laminated. The photosensitive layer has a charge generating layer, which mainly has the function of charge generation when receiving light, and a charge transporting layer, which has the function of maintaining surface charge in the dark and of transporting the charge generated in the charge generating layer when receiving light. In recent years, the function-separated laminated organic photosensitive body has become mainstream.
The manufacturing method for this photosensitive body uses organic pigment as the charge generating material. A coating solution, in which this organic pigment is dispersed and dissolved in an organic solvent, together with a resin binder, is coated to form a film to become the charge generating layer. Using an organic low molecular weight compound as the charge transport material, a coating solution, in which this compound together with a resin binder is dissolved in an organic solvent, is coated to form a film to become the charge transport layer. These are laminated to form the photosensitive body.
However, currently, the organic photosensitive body does not always adequately satisfy the desired properties of a photosensitive body. The following various problems have been raised.
First, one of the properties which has been eagerly sought after is an improvement in the stability of the electric property when using repeatedly. Stated more concretely, when the photosensitive body is being continuously and repeatedly used in a real machine, there is fluctuation in the electric potential (particularly the light electric potential), and this invites a deterioration in the copy image quality and print quality. The reasons for such an electronic potential fluctuation include fatigue and deterioration of the organic material due to light, heat, ozone generated with the continuous use inside the real machine, or due to changes in the temperature and humidity conditions of the usage environment.
Furthermore, in real machines such as copiers, digital copiers, printers, and the like, particularly when conducting continuous printing, there can be a so-called memory phenomenon where a developed image can appear in places where there is no printing. This can cause problems as an image defect. Particularly under low temperature/low humidity or high temperature/high humidity conditions, the generation of memory is an important problem that needs to be addressed. With regard to this memory generation, it may be due to the storage in the organic film of charge which is generated during the process of light exposure or charge removal of the photosensitive body, or it may be due to the trapping of charge in the charge transport layer or at the interface of the charge generating layer and the charge transport layer. Currently, there has been progress in improving each of the charge generating material and charge transport material.
These various problems relating to the photosensitive bodies have been studies a great deal, and there have been new proposals, but there is still no means or materials for adequately solving the problems.